1. Technical Field
The present invention relates to an endoscope.
2. Description of Related Art
An endoscope is typically furnished with a manipulation unit, and an insertion unit which is disposed in continuation to the manipulation unit. The insertion unit includes a bending portion, and a distal end portion which is provided in continuation to the distal end side of the bending portion. The distal end portion is provided with an imaging apparatus including a solid-state imaging element, an illuminating optical system, etc., and it images the part tobe-observed of a subject. The bending portion has a plurality of articulation wheels which are coupled in succession, and the two adjacent ones of which are coupled by a pin orthogonal to a center axis of the bending portion, so as to be relatively turnable around the pin. In addition, a wire which leads to the manipulation unit via the articulation wheels is laid. The wire is tractively manipulated, whereby the bending portion is bent, and the distal end portion is deflected in a predetermined direction.
In the endoscope wherein the distal end portion is deflected in the four directions of upward and downward directions and rightward and leftward directions, a pin which couples the two adjacent articulation wheels is arranged so as to alternately extend in a first direction orthogonal to the center axis of the bending portion, and a second direction orthogonal to the center axis of the bending portion and also orthogonal to the first direction. Besides, four wires are laid along the center axis of the bending portion at intervals of about 90 degrees around this center axis. Insertional holes which penetrate in the axial direction of the bending portion are formed at the distal end parts of the pin, and the respective wires are disposed so as to successively pass through the insertional holes of the pin arrayed in the axial direction of the bending portion.
The coupling place between the two adjacent articulation wheels is configured in such a manner that coupling parts provided in both the articulation wheels are placed one over the other double inside and outside, and that the pin is inserted through pin holes which are respectively formed in both the coupling parts. The pin is caulked to the coupling part of one articulation wheel located outside, and it is secured to this coupling part. On the other hand, the pin is loosely fitted in the coupling part of the other articulation wheel located inside. Therefore, the other adjacent articulation wheel turns around the pin relative to one articulation wheel to which the pin is secured (refer to, for example, JP-3835077-B).
In the endoscope of the structure of JP-3835077-B stated above, when the two adjacent articulation wheels have been relatively turned, the inflection of the wire hardly occurs at the edge of the insertional hole facing to one articulation wheel to which the pin is secured, but a conspicuous inflection can correspondingly occur in the wire at the edge of the insertional hole facing to the other articulation wheel. Therefore, a force which acts on the wire by the touch thereof with the pin concentrates on that part of the pin which touches the edge of one of the insertional holes, and the wear of the wire at the part becomes conspicuous.